This invention relates to a display panel having erasable images thereon which can be projected or viewed directly. More particularly this invention relates to flat PLZT display panels wherein one side of the PLZT panel contains metallized islands within a grounded metallized grid pattern. The PLZT material located between an island and the grid pattern defines a pixel or image forming element which is utilized to form an image on the PLZT plate by means of birefringence.
U.S. Pat. No. 3,666,666 discloses a fine grain, polycrystalline, ferroelectric, ceramic material that exhibits birefringence, i.e., upon the application of an external electric field in the plane of the material, the material decreases its index of refraction along the electric field vector to produce two orthogonal axes with an index of refraction difference. The birefringence retards the phase of linearly polarized light and thus can be used to vary the transmission through a suitably oriented polarization analyzer. The specific compositions of ferroelectric ceramic materials which do not exhibit remnant polarization and which are characterized as a slim loop material, are best suited for operation with surface electrode pattern induced birefringence. The ferroelectric ceramic in the U.S. Pat. No. 3,666,666 contains lanthanum doped lead zirconate-lead titanate (hereinafter referred to as PLZT material). Due to its unique optical characteristics, PLZT material has been used to perform various functions in the field of optics. For example, U.S. Pat. No. 3,612,656 discloses a PLZT plate device which is utilized as an optical shutter, i.e., the PLZT plate device is either opened or closed to the transmission of polarized light. U.S. Pat. No. 3,531,182 discloses the use of a plurality of crossed conductors to control the birefringence of discrete areas of a plate of PLZT material to provide an array of light shutters that may function as information storage areas. U.S. Pat. No. 3,702,215 discloses a system wherein a bare PLZT plate is scanned by an electron beam in a vacuum to produce an erasable image that may be projected. In addition to the disadvantage of being operable only in a vacuum, the system disclosed in the U.S. Pat. No. 3,702,215 has the added disadvantage that the bare PLZT device does not contain surface electrode patterns or image forming elements on the surface of the PLZT plate, and therefore does not form birefringence images with the slim loop PLZT material.
One object of this invention is to provide a flat display panel that utilizes a PLZT plate on which erasable images can be formed for direct viewing or projection.
Another object of this invention is to provide a flat display panel that utilizes a PLZT plate having a plurality of metallized islands thereon which are surrounded by a metallized grid pattern to enable erasable images to be formed on the PLZT plate which may be viewed directly or projected.
Still another object of this invention is to provide a flat display panel that utilizes a PLZT plate having a plurality of electrically conductive islands thereon which are surrounded by an electrically conductive grid pattern that enables erasable images to be formed on the PLZT plate either electrically or optically.
A further object of this invention is to provide methods of forming and erasing images on a PLZT plate having metallized islands deposited thereon and surrounded by a grounded metallized grid pattern.